1. Field of the invention
Environmental considerations have caused electric public utility companies to install non specular finish bare stranded conductor (also called cable) in overhead distribution and transmission electrical power lines. The non specular surface finish for bare stranded aluminum and aluminum steel reinforced conductor is described in American National Standard C 7.69. A segment of the public objects to seeing overhead power lines.
2. Description of the prior art
The non specular finish commonly used for many years, and now, is obtained by passing the otherwise completed conductor thru an abrasive blasting machine. A typical such abrasive blasting machine is one commonly used for removing mill scale from pipe. This is done as the last process before the conductor is wound onto reels for shipment from manufacturer to user.
Government specifications have limited the acceptance of non specular surface finish bare stranded electrical conductor to that which has "a surface condition when received at the delivery point to be clean and free of sharp edges, scratches, grit, corrosion, excess drawing lubricant and other contaminants".
The effect of entrapped jet blasted abrasive grits on the interior strands of multilayer conductor has been dismissed an unavoidable - one just has to live with this entrapped grit because of the need to manufacture a non specular surface conductor for environmental aesthetic considerations.
Such conductor wears in an outdoor overhead power line installation. Each individual strand is constantly being minutely slided relative an adjacent strand. This constant movement among adjacent strands is due to the wind caused aeolian vibrations. Infrequent galloping of he conductor, as well as expansion and contraction of the conductor due to temperature changes, also causes sliding between adjacent strands.
Each layer of such a multilayer conductor must be so stranded that the completed conductor is flexible. Otherwise it could not be wound onto reels for shipping and installation, nor sagged for strength of installation, nor able to withstand wind and temperature conditions during service. Thrasher for example, is so stranded in the top layer that there is about 1/8 inch in circumference total looseness between strands. Too tight and the conductor is not sufficiently flexible -- too loose and it basket-weaves. The required looseness in stranding permits abrasive blasting grits in current methods of making the conductor surface finish non specular to penetrate to interior strands and become permanently embedded or entrapped.
All entrapment of grit caused by the jet grit blasting process currently used is not removable by cleaning. So entrapped grit has been so wedged in entrapment that it cannot be removed by blowing or suction air pressure, or by any known method without destroying the conductor. The abrasive grits used have been commercial blasting grits, including silica sand, aluminum oxide, glass and garnet of about 100 to 300 mesh.
In one sample of new Bluebird non specular finish conductor as now manufactured, the following weight of garnet grit was found remaining from the manufacturing process (in pounds/thousand feet): top layer 0.870; second layer 0.975; third layer 0.195; fourth layer 0.053; steel core 0.012; and total weight being 2.105.
In one sample of new Thrasher non specular finish conductor as now manufactured, the following weight of garnet grit was found remaining from the manufacturing process (in pounds/thousand feet); top layer 0.363; second layer 0.534; third layer 0.041; fourth layer 0.001; steel core 0.002; and total weight being 2.105.
Overhead stranded bare power lines wear out because of weathered particles blown by winds into the conductor during there service life. The abrasive grit particles entrapped during the current manufacturing method for making non specular finish bare stranded conductor causes additional wear during its service life. These grit abrasives are deeper penetrated, sharper, harder, greater in quantity, and more damaging than the wind blown in particles during the service life. Conductor life is thereby shortened. No one knows by how much such conductor life is shortened. The amount and distribution of such permanently by manufacturing process embedded abrasive grits in thousands of miles of conductor so made is unknown. The invention herein solves the problems in the prior art caused by entrapment of abrasive grit particles during manufacture.